A common problem where light is coupled into an optical fiber is that there is a loss of light. For instance, even with careful design to match the input numerical aperture to that of the fiber, there is usually a lateral or angular misalignment with respect to the downstream fiber. This misalignment can result in light being coupled into the cladding rather than into the core, as intended. Light escaping from the core is commonly referred to as cladding mode light, or simply cladding light.
Cladding light can be present in a variety of devices: a laser diode, a splice, in a free space optical device, or a tapered fiber device. Cladding light can also appear in intentionally bent fiber, in periodical structures, such as fiber gratings, or at inadvertent micro-bends in a fiber. It is desirable to remove the cladding light before the next discontinuity in the fiber path for a number of reasons, among them because the cladding light can couple back into the fiber's core, generating multi-path interference.
The removal of cladding light, however, can cause unacceptable heating within an apparatus containing or coupled to the optical fiber. In particular, heating caused by the dissipation of cladding light can be very detrimental to the operation of high optical throughput apparatus. This problem is becoming increasingly important as the industry trends toward high power applications. As the amount of power carried in optical fiber increases from levels of a few watts up to kilowatts, conventional approaches to remove cladding light become inadequate.
For example, the removal of cladding light into polymeric coatings can be problematic in high power applications where the amount of cladding light is greatly increased. The removal of such light can cause excessive heating of the polymer coating as it absorbs the light, causing accelerated aging, and sometimes failure, of the coating and then the fiber. Additionally, in situations where the use of a polymer coating is unacceptable, there can be insufficient space in a device package to couple adequate numbers of heat sinks to the optical fiber to dissipate heat.
The present invention overcomes these problems by providing a light guiding structure in a glass cladding that facilitates the controlled dissipation of heat associated with the removal of cladding light from an optical fiber.